First and foremost find out what your reception site does and doesn't alloww/provide. What are the requirements for setup and breakdown?
Secondly, decide on how much you can afford to spend on food and beverages. Add about 10% for overages and include extra funds for gratuities.
Important Questions to ask
Does the caterer specialize in certain types of food?
Does the price include table linens, plates and glassware? Do you have to rent this equipment yourself or will they arrange for the rentals?
Does the caterer set the tables? Will they put out place cards and favors?
Will the caterer provide wait staff? How many? What will the wait staff wear?
Will they make provisions for guests with special dietary needs (Vegetarian, cholesterol)? Will smaller meals be provided for the disc jockey (or band), photographer, and videographer?
Does the caterers offer hors d'oeuvres? At what cost? What is the price difference between having them served by wait staff verse displaying them on a buffet table?
Does the caterer also do wedding cakes? Can you use an outside baker? Is there a cutting fee? (This is often charged when you buy the cake and ask the caterer to serve it).
Can the caterer provide alcohol? Or can you handle the bar separately? Does the caterer charge a corking fee if you buy the alcohol from someone else?
Will the food be prepared on-site or do other arrangements need to be made?
Is there a gratuity charge?
Who is your contact? Will this same person also oversee service at your wedding?
How involved is the caterer in a typical reception - does he or she work like a wedding coordinator/banquet manager, cueing the band, telling you when to cut the cake, adjusting the schedule if guests don't seem ready to sit down and eat? (You will need to find someone to fill this role-if your site manager or caterer does not do this - hire a wedding coordinator).
What does the caterer do with leftover food?
Since you're paying for it, you may want to have it boxed up or
donated to a local charity.
Is the caterer state-licensed? Do they have liability insurance and a valid liquor license?
How long has the caterer been in business? Are they affiliated with
any professional groups or societies? Can they provide you with
a list of recent references to check?
How much leeway do you give over the final head count? Will you
be able to make a few extra or fewer meals if we have last-minute
guests or no-shows?
Finally, make sure to clearly outline the caterer's responsibilities, from the specific food and quantities down to who cleans up after the party. Put it in writing and get it signed.